Technical Field
This application generally relates to caching techniques and more particular to cache update techniques.
Description of Related Art
Computer systems may include different resources used by one or more host processors. Resources and host processors in a computer system may be interconnected by one or more communication connections. These resources may include, for example, data storage devices such as those included in the data storage systems manufactured by EMC Corporation. These data storage systems may be coupled to one or more servers or host processors and provide storage services to each host processor. Multiple data storage systems from one or more different vendors may be connected and may provide common data storage for one or more host processors in a computer system.
A host processor may perform a variety of data processing tasks and operations using the data storage system. For example, a host processor may perform basic system I/O operations in connection with data requests, such as data read and write operations.
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units, disk drives, and disk interface units. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical disk units. The logical disk units may or may not correspond to the actual disk drives. Allowing multiple host systems to access the single storage device unit allows the host systems to share data in the device. In order to facilitate sharing of the data on the device, additional software on the data storage systems may also be used.
In connection with data storage systems, or more generally any type of system, caching may be used whereby data of the cache may be used to service operations rather than data as may be stored on a slower storage medium, such as disk. When a requester requests data, there may be considerable latency incurred in the process of retrieving the data from the disk. A cache may store data in a memory characterized as a relatively fast memory that is separate from the disks in order to address some of the latency issues associated with disks. The cache memory may contain some or a portion of the data as stored on the disk. Upon receiving a request, for example, to read data, the data storage system may service the request using the cached data if such requested data is currently in the cache.